Without limiting the scope of the invention, its background is described in connection with hydrogels. Hydrogels are generally polymer chain networks that are water-insoluble, but that absorb water. Often described as being “superabsorbent,” hydrogels are able to retain up to 99% water and can be made from natural or synthetic polymers. Often, hydrogels will have a high degree of flexibility due to their high water content. Common uses for hydrogels include: sustained drug release, as scaffolds (e.g., in tissue engineering), as a thickening agent, as a biocompatible polymer, in biosensors and electrodes and for tissue replacement applications. Natural hydrogels may be made from agarose, methylcellulose, hyaluronic acid (HA), and other naturally-derived polymers.
One method for making hydrogels is a taught by U.S. Pat. No. 7,307,132, issued to Nestler, et al., for a method of producing low-odor hydrogel-forming polymers. Briefly, a low-odor hydrogel-forming acrylic acid polymer is prepared by preparing a polymeric hydrogel by free-radically polymerizing a monomer composition comprising at least 50% by weight of acrylic acid in an aqueous polymerization medium and converting said hydrogel into a particulate hydrogel or into hydrogel-forming powder; and optionally treating the particulate hydrogel or said hydrogel-forming powder with a crosslinking substance which, actually or latently, contain at least two functional groups capable of reacting with the carboxyl groups on the addition polymer; characterized by the acrylic acid used in step (a) containing less than 400 ppm of acetic acid and propionic acid.
Another method is taught by U.S. Pat. No. 6,943,206, issued to Haraguchi for an organic/inorganic hybrid hydrogel and method for manufacturing. Briefly, an organic/inorganic hybrid hydrogel is said to have superior homogeneity, transparency, mechanical properties, and swelling and shrinking properties. A dry body of the organic/inorganic hybrid hydrogel is obtained by removing water from said hydrogel. The organic/inorganic hybrid hydrogel comprises a water soluble polymer (A), a water swelling clay mineral (B) which can be homogeneously dispersed in water, and water (C), and water (C) is included in a three-dimensional network formed by (A) and (B).